Controlling flies on pastured cattle

With record setting temperatures this spring insects are making an earlier appearance this year. Horn flies, face flies and even stable flies have been observed on grazing animals recently.

Normally we do not think about livestock pest control this early in spring, but this year appears to be different. As livestock producers ponder when to send cattle to pasture another consideration is what livestock pest control options are available for this summer. Livestock pest control should be viewed as having a positive economic impact on your livestock operation.

There are three fly species in Nebraska that economically impact pastured cattle: horn fly, face fly and stable fly.

Horn Fly

The horn fly, Haematobia irritans (L.) is one on the most important blood feeding pests of pastured cattle in the United States. Losses in the United States have been estimated at about $800 million annually. When horn fly numbers are high, cattle experience annoyance and blood loss (see image at right, click on image for larger view). The result may be decreased milk production, reduced weight gains, changes in grazing patterns and bunching of animals. Significant reduction in calf weaning weights is well documented. Nebraska studies demonstrated calf weaning weights were 10 to 20 pound higher when horn flies were controlled on cows. Other studies around the U.S. and Canada have shown improved weight gains of stocker cattle and replacement heifers when comparing treated to untreated animals. In addition, horn flies have been implicated in the spread of mastitis.

The economic threshold for horn flies is 200 per animal. The animal pictured at right has 314 horn flies and population numbers of several thousand of flies can often be observed during the summer. Monitoring horn fly numbers on cattle is important in making appropriate management decisions. Routine observations will help livestock producers determine when best to initiate control methods and the efficacy of the current program. Cattle should be be monitored weekly for horn flies throughout the fly season. Observations are best taken between the hours of 9:00 AM - 1:00 PM when horn flies are located on the shoulders and sides of cattle. Observations made later in the day are less accurate because the flies will have moved to the belly where it is cooler and where they are harder to count. If the average number horn flies per animal exceeds 200 (Figure 2), the economic threshold has been exceeded and control should be considered.

The horn fly is a blood feeding fly that is located on the shoulders, back and belly region of cattle, they take some 20 to 30 blood meals per day and the only time they leave an animal is when the female deposits eggs in fresh cow manure. The complete life cycle, egg to adult, can be completed in 10 to 20 days during warm conditions. In Nebraska, where we typically have several generations during the summer horn fly populations can reach very high levels.

Animal sprays can be an effective way on reducing horn fly numbers. Drawbacks with animal sprays are increased cattle handling, cost, and added stress to the cattle during the fly-season. Control products recommended as animal sprays are: coumaphos (Co-Ral), permethrin (many brand names) natural pyrethrins, and phosmet (Prolate).

Oral larvicides and insect growth regulators (IGR) prevent horn fly larvae from developing into adults. These can be delivered to cattle as loose mineral, mineral blocks or tubs. To be effective cattle must consume a specified amount of product per day. Proximity to untreated cattle and inadequate consumption by cattle are two factors that can contribute to poor fly control. Products recommended are: diflubenzuron (Clarify), methoprene (Altosid), and tetrachlorovinphos (Rabon).

Pour-on insecticides are ready-to-use formulations applied along the back line of cattle. Although pour-ons will control flies for short periods, the stress in cattle in using this method may offset the benefits of the fly control. Many pour-on insecticides are synthetic pyrethoids, however, a few pour-on insecticides are macrocyclic lactones (ivermectin, etc,). Products recommended are: permethrin (many brand names), macrocyclic lactones (ivermectin and related compounds), and spinosad (Elector).

Insecticide impregnated ear tags contain one or more insecticides embedded in a plastic matrix. The insecticide ear tag was first developed in the early 1980s, and worked very well against horn flies. However within a few years, horn flies developed resistance to synthetic pyrethroid insecticides. To maintain efficacy, specific steps should be taken to manage resistance. These include: A) rotation of insecticide classes, do not use the same insecticide class year after year, B) withhold tagging until horn fly numbers reach 200 per animal, C) tag all adult cattle in the herd and with the recommended label rate, D) use alternative insecticides and application methods late in the season; and E) remove insecticide ear tags in the fall. Ear tags recommended are: Organophosphtes (Corathon,™ Optimizer,™ Patriot,™ and Warrior™) Synthetic Pyrethroid (CyGuard,™ Gardstar Plus,™ PYthon,™ PYthon MagnuM,™ and Saber Extra,™ Double Barrel™VP) Macrocyclic Lactone (XP 820™).

Recent studies in Nebraska (Fig. 1 below) illustrate the performance of selected ear tags against horn fly populations. Ear tag efficacy declined over time but the point where the economic threshold was exceeded varied among the products tested.

To achieve the maximum performance from an insecticide ear tag, two tags per animal are required, and delaying ear tagging until June 1st will provide a producer with the greatest degree of horn fly control. A livestock producer in Nebraska can expect 12 to 14 weeks of horn fly control if the aforementioned methods are utilized.

Face Flies

The face fly, Musca autumnalis (DeGeer), is a robust fly that superficially resembles the house fly. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. Adult female face flies typically cluster around the animals' eyes, mouth, and muzzle, causing extreme annoyance. They are also facultative blood feeders, meaning that they gather around wounds caused by mechanical damage or other injury to feed on blood and other exudates. Because face flies are on animals for only short time periods they are difficult to control. Most of the time they are found resting on plants, fence posts and other objects.

In addition to being very annoying to cattle, face flies vector Moraxella bovis, the principal causal agent of bovine pinkeye or infectious bovine keratoconjunctivitis. Pinkeye is a highly contagious inflammation of the cornea and conjunctiva of cattle. If coupled with the infectious bovine rhinotracheitis (IBR) virus, M. bovis can cause a much more severe inflammatory condition.

Control

Controlling face fly numbers is a key to reducing pink-eye problems. Fly control methods described in the discussion of the horn fly can be used against the face fly. Insecticide ear tags appear to provide a higher degree of face fly control. Please use the label recommended rate of application. Both cows and calves must be treated if control is to be achieved. In respect to pink-eye vaccines, commercial and autogenous pinkeye vaccines are available. Please check with a local veterinarian about the use of these products in a specific geographical area.

Stable Flies on Pastured Cattle

Stable flies, Stomoxys calcitrans (L.), are pests of cattle on pastures in the Midwest. Stable flies mainly feed on the legs of cattle. To avoid being bitten, animals stomp their feet and switch their tails. Other avoidance behaviors include standing in water, lying with legs tucked underneath and bunching at the corners of pastures.

The effect of stable flies on weight gain performance of pastured cattle is similar to that of livestock in confined operations. Research conducted at the University of Nebraska, West Central Research & Extension Center recorded a reduction in average daily gain of 0.44 lb per head per day in 84-day trials compared to cattle that received an insecticide application. The economic threshold of five flies per leg is easily exceeded in Nebraska pasture conditions.

The stable fly is about the size of a house fly but is dark gray and has dark irregular spots on its abdomen. The proboscis (mouthpart) protrudes bayonet-like in front of the head. The larvae are typical whitish fly maggots. The pupae are chestnut brown and about 1/4 inch long. The complete life cycle of the fly from egg to adult can take 14-24 days in Nebraska during hot weather. While the source of early season flies is not well understood some probably develop from overwintering maggots. Other early season flies may be migrants from southern locations but definitive evidence of migration is lacking. However, we do know that stable flies can move at least 10 miles or more.

The female fly deposits eggs in spoiled or fermenting organic matter mixed with animal manure, moisture and dirt. The most common breeding sites are in feedlots or dairy lots, usually around feed bunks, along the edges of feeding aprons, under fences and along stacks of hay, alfalfa and straw. Grass clippings and poorly managed compost piles also may be stable fly breeding areas.

Control

The only management option available for control of stable flies on range cattle is use of animal sprays. Products such as coumaphos (Co-Ral), permethrin (many brand names), natural pyrethins (many brand names), and Phosmet (Prolate) are available for use. Clean-up of wasted feed at winter feeding sites may prevent localized fly development but may not reduce the economic impact of stable fly feeding.

When applying any insecticide control products please read and follow the label instructions.